Sonic reflectors are known in the art. Historically sonic reflectors have been divided into generally two basic categories: one group being so-called low-pressure reflectors finding utility in marine environments of modest depth; the other group being configured for operation at greater depths.
With respect to the former group, such baffles are often formed from rubber having air-filled cells therein or, alternately, thick sheets of rubber covered metal. For deep water marine environments, sheets of rubber having air-filled cavities therein tend to lose effectiveness, at least in part because of elevated hydrostatic pressures encountered and in part due to long immersion. Thick rubber covered plates in such deep water environments may be difficult to tune and through sheer bulkiness can provoke operational difficulties particularly where it is desired that low frequencies be reflected.
One high pressure baffle configuration finding acceptance in a deep water environment is a so-called squashed-tube configuration. Squashed-tube baffles are shown and described, for example, in U.S. Pat. No. 3,021,504 (Toulis). Squashed-tubes are typically formed by compressing a metallic tube into a permanently deformed ovaloid configuration. Such deformed tubes may then be grouped in bundles oriented to have longitudinal axes thereof generally parallelly coplanar, or otherwise oriented to define a curvilinear surface formed of the generally parallelly oriented squashed-tubes.
In addition, it has been determined that such squashed-tubes may be oriented in ranks, squashed-tubes within a particular rank being generally parallelly oriented, and the ranks may be applied to the surface of vessels such as submarines in order to shield sonic arrays mounted thereover from sonic interference emanating from within the vessel.
It is known that such squashed-tubes may be encapsulated in rubber. Encapsulation can assist in assuring against water infiltration into the squashed-tube with consequent, attendant, disruption of reflecting or baffling capability. Depending upon the nature and construction of the rubber encapsulant, encapsulation can assist in enhancing reflection or baffling characteristics associated with a squashed-tube array.
Frequently in applying squashed-tube baffle arrays to an external surface of a vessel, it may be desirable to utilize more than a single rank of such squashed-tubes with each rank being a series of squashed-tubes arranged to define a sheet-like formation in a plane generally Parallel to an external surface of the vessel, squashed-tubes in each rank being of a different physical size. This difference in physical size of the tubes forming each rank assists in baffling or reflecting different sonic frequencies. Both the width of individual tubes between different arrays may vary, and the thickness of metal walls defining the tubes may vary from rank to rank to enhance a capability for the array handling a variety of sonic frequencies.
In deep water marine environments, the squashed-tubes respond to increasing hydrostatic pressure as a submersible embodying an array of such squashed-tubes descend through the depths. In response to increasing hydrostatic pressure the tubes flatten even more at the greater marine depths, but typically maintain a pocket of air therein to continue a reflector or baffling function. At extreme depths, the squashed-tube may flatten to the extent that center portions of the long radius curvilinear surfaces of the ovaloid defined by the tube touch one to the other thereby mechanically supporting the squashed-tube in some measure against additional collapse.
Where the squashed-tubes have been formed from a relatively spring-like or elastic material, that is one tending to return to a physical configuration characterizing the tube prior to hydrostatic compression, the squashed-tubes, with a rise of the submersible from great depths will resume their previously ovaloid configuration.
The manner in which compliant tube arrays formed from squashed-tubes function in reflecting or baffling acoustic frequencies can be described mathematically. While the mathematics of predicting precisely the behavior of a squashed-tube array can be tedious at best, certain approximations are available in the art for predicting the approximate performance of a particular squashed-tube array. One such prediction method is described in an article entitled Water-Borne Sound Insertion Loss of a Planar Compliant-Tube Array published in J. Acoust. Soc. AM. 78 (3), September 1985 and authored by M. C. Junger.
The Junger prediction is based upon a flat-plate model of an array having flat-plate surfaces associated with tubular members of the array; arrays formed from squashed-tubes, in part because of their ovaloid configuration, do not approach the acoustic performance predicted by a flat plate model as accurately as, perhaps, array formed from essentially flat plate structures may.
Additionally, where squashed-tubes become excessively deformed by exposure to unexpectedly elevated hydrostatic pressures, the squashed-tubes may become to some extent permanently deformed from a naturally ovaloid configuration thereby permanently interfering with a capability for an array of the squashed-tubes to Perform satisfactorily as a baffle or reflector.
A baffle formed of an array of tubular structures having a flat plate general configuration, the behavior which is substantially predictable employing relatively simple prediction models, could find utility in deep water applications. Where such baffles can be formed economically employinq readily available materials, and are less susceptible to crush damage from inadvertent exposure to excessive hydrostatic pressures, the Potential utility is even greater.